People increasingly demand packaging materials that protect their contents better especially in the food and pharmaceutical industries, but now also in other industries such as agricultural chemicals, electronics and healthcare. As plastic have become more and more common in these applications, there have been many concerns about how well they allow the exchange of gases and vapours that can compromise the quality and safety of the packaged product. Presence of oxygen, by direct chemical reaction or as enabler of spoiling bacteria, is one of the main sources of spoilage of goods that, in the modern economy, are transported from one point of the earth to the other or stored for long periods of time. Consequently, the packaging industry has long attempted to displace the oxygen inside packages, replacing it with inert gases (modified atmosphere packaging, MAP), and to block the passage of oxygen from the outside to the inside of such packages using passive barrier materials with low permeability to oxygen. Even if each of the above techniques has its place in the industry, it is well recognized that the inclusion of an oxygen scavenger as a part of the packaging article is one of the most desirable means of limiting oxygen.
The problem is particularly felt for PET (polyethylene terephthalate), which is in itself a good passive barrier to oxygen and is the packaging material of choice especially for beverages. A number of technologies have been devised to scavenge the low concentration of oxygen able to pass the PET passive barrier, and therefore granting an actually oxygen-free period of time for the package content. In general, such technologies are based on the catalyzed oxidation of compounds additivated to the main polymer or as/in separate co-extruded layers, without resorting to any activation mechanism. They rely on an efficient transfer of the packaging material from the manufacturer to the final industrial user to address the issue of exhaustion of the active component by reaction with atmospheric oxygen, with inconsistent results.
Other schemes have been devised that instead rely on some activation mechanism that sets the moment when reaction with oxygen of the scavenging chemistry begins to occur at a different point in time than the manufacture of the packaging plastic. In the system sold by Sealed Air, for example, such activation is achieved by UV irradiation on the packaging line, which must be modified to use this system. Activity and safety concerns are also present. The Fe-based chemical additive now commercialized by Albis (previously by Ciba Specialty Chemicals), instead, relies on the water present in the packaged item itself as the trigger for the oxygen scavenging process. However, such water requirement is substantial, and the quantity of additive necessary for sufficient activity notably darkens even thin plastic sheets. Such effect is undesirable since consumers prefer being able to see clearly the food contained inside the package they are buying.
Another approach to achieving or maintaining a low oxygen environment inside a package is to use a packet containing an oxygen absorbent material. The packet, also sometimes referred to as a pouch or sachet, is placed in the interior of the package along with the product. Sakamoto et al. discloses oxygen absorbent packets in Japan Laid Open Patent application No. 121634/81 (1981).
Although oxygen absorbent or scavenger materials used in packets, as reduce iron powder, sodium chloride electrolyte system and water absorbing agent such as silica gel, can react chemically with oxygen in the package (head space oxygen), they do not prevent external oxygen from penetrating into the package. Thus for such type of packaging it is common to include additional protection such as wrappings or passive barrier films (ethylene vinyl alcohol copolymer EVOH, polyvinylidene dichloride PVDC, etc. . . . ) which inevitably add costs to product. Furthermore with many easy to prepare foods, another difficulty with oxygen scavenger packets is that consumers may mistakenly open them and consume their contents together with food. Moreover, the extra manufacturing step of placing a packet into a container can add to the cost of the product and slow down production. Further, oxygen absorbent packets are not useful with liquid products.
Therefore, none of the systems currently available possess all the characteristics to satisfy the stringent market requirements for the packaging of fresh or prepared foods.
The current invention addresses some of the issues limiting the exploitation of this useful technology.
An object of the present invention is therefore to provide improved oxygen-scavenging compositions and packagings. Another object is to provide low costs, oxygen-scavenging compositions of improved efficiency. Another object is to provide oxygen scavenging composition that can be used effectively, even at relatively low levels, in a wide range of active-barrier packaging films and sheets, including laminated and coextruded multilayer films and sheets. Another object is to provide active-barrier packaging containers that can increase the shelf-life of oxygen-sensitive products by slowing the passage of external oxygen into the container, by absorbing oxygen present inside the container or both. Other objects will be apparent to those skilled in the art.
It has been observed that the use of the inventive oxygen-scavenging composition enhances the resistance of the packed food products against the oxygen attact.
Thus the present invention relates to an oxygen scavenger composition for food packaging application comprising
(I) A polymeric resin preferably a thermoplastic polymers
Homo and copolymers of olefin monomers such as ethylene and propylene, but also higher 1-olefins such as 1-butene, 1-pentene, 1-hexene or 1-octen. Preferred is polyethylene LDPE and LLDPE, HDPE and polypropylene;
Homo- and copolymers of olefin monomers with diolefin monomers such as butadiene, isoprene and cyclic olefins such as norbornene;
Copolymers of one or more 1-olefins and/or diolefins with carbon monoxide and/or with other vinyl monomers, including, but not limited to, acrylic acid and its corresponding acrylic esters, methacrylic acid and its corresponding esters, vinyl acetate, vinyl alcohol, vinyl ketone, styrene, maleic acid anhydride and vinyl chloride;
(II) A metal organic oxidation additives based on a chelating aromatic or non aromatic amine and transition metal complex as defined in the examples below. These organic metal oxidation additive complexes are generally based on Co, Ce, Mn, Cu, Ni, Vd, Fe, Ti. Preferably these nitrogen ligand oxidation additives are metal salts of fatty acids with a carbon number raging from C12 to C36. Most preferred are metals carboxylates of palmitic (C16), stearic (C18), oleic (C18), linolic (C18) and linoleic (C18) acid. Preferably the transition metal salt is Manganese, Copper, Iron or Cobalt and most preferably Manganese or Copper which may be present in a total concentration from 0.001-10 wt %, preferably 0.01-5 wt % and most preferably 0.1-5 wt % based on the polymeric resin. Also possible are metal salts of propionic (C3), acetic (C2), formic (C1) or benzoic acid. It is also possible that the counter ions in the metal complexes are halogens and preferably but not limited to chloride, bromide and Iodide. The oxidation additive(s) may be present in total in a concentration from 0.001-10 wt %, preferably 0.01-5 wt % and most preferably 0.1-5 wt % based on the polymeric resin;
(III) Sacrificial oxidizable substrates like polybutadiene, polyester, squalane, squalene, polystyrene, poly-limonene, poly alpha pinene, poly beta pinene, polynorbornene, polylactic acid, mixture of linear and branched alkyl chains alcohol (R: C6-C30). Preferably these oxidizable substrates are present in a total concentration from 0.001-10 wt %, preferably 0.01-5 wt % and most preferably 0.1-5 wt % based on the polymeric resin;
(IV) additional components.
The metal organic oxidation catalysts of this invention relates to a metal complex compounds of formula
Me is manganese, copper, cobalt, nickel, iron, cerium, vanadium or titanium
X is a coordinating or bridging radical
n and m are each independently to each other an integer having a value from 1 to 8
p is an integer having a value from 0 to 32
z is the charge of the metal complex
Y is a counter ion
q=z (charge Y), and
L is a ligand of formula:
R1, R2, R3, R4, R5, R6, R7, R8 and R9 are each independently of the others hydrogen; unsubstituted or substituted C1-C18 alkyl or aryl; cyano; halogen; nitro; —COOR10 or —SO3R10 wherein R10 is in each case hydrogen, a cationic or unsubstituted or substituted C1-C18 alkyl or aryl; —SR11, —SO2R11 or —OR11 wherein R11 is in each case hydrogen or unsubstituted or substituted C1-C18 alkyl or aryl; —N(R11)—NR′11R″11 wherein R11, R′11 and R″11 are as defined above for R11; —NR12R13 or —N+R12R13R14 wherein R12, R13 and R14 are each independently of the other(s) hydrogen or unsubstituted or substituted C1-C18 alkyl or aryl, or R12 and R13 together with the nitrogen atom bonding them form an unsubstituted or substituted 5-, 6- or 7-membered ring which may optionally contain further hetero atoms;
and wherein G is phenyl or naphthyl unsubstituted or substituted C1-C6 alkyl, C1-C6 alkoxy, halogen, cyano, nitro carboxyl, sulfo, hydroxyl, amino, N-mono- or N,N-di-C1-C6 alkylamino unsubstituted or substituted by hydroxyl in the alkyl moiety, N-phenylamino, N-naphthyl-amino, phenyl, phenoxy or naphthoxy. Preferred substituents are pyridyl, imidazole or piperidine groups,
Particularly preferred are the compounds given in the following tables: